How to randomize wood pattern in many object?
so you can use object info node for this!

just add a mix rgb node and put the image texture in the first node and a color ramp in the second one. just choose some shades of grey in the ramp. you might want to choose similar types of shades. just vary them a little( my colors are too drastic).

no each copy of the wood mesh will have different color due to the mixing. rememder to make the wood meshes different objects(duplicate them in object mode not in edit mode).



Now to vary the wooden pattern, yoou can scale he uvs differently and get different patterns, just move the uvs randomly and scale them a litle. remember to use UV coordinates in your image texture.

you can combine both methods to get different looking wood materials.